The present invention relates to a printing method and a printing press, and particular to a printing method with no penetration of a dampening water into an area of an on-press type printing plate at which the printing plate is gripped and fixed, and a printing press employed the method.
Recently, a printing press equipped with an image forming means represented by an infrared laser irradiation device, so-called a DI printing press, has been focused on as a system for prompt delivery of prints and reduction of printing cost. As the DI printing press, there are a printing press employing a dampening water and a waterless type printing press employing no dampening water, as in an ordinary printing press.
The waterless type DI printing press has no device supplying a dampening water, and if equipped with an image forming means, it can provide a compact construction. For example, printing presses such as Quickmaster-46-DI produced by Heiderberg Co., Ltd and 3404DI produced by Ryobi Co., Ltd. have advantages that they can be installed anywhere in a reduced space, although they have a means for storing a printing plate precursor (hereinafter referred to also as a plate precursor) in the roll form within a cylinder, means for winding the plate precursor around the cylinder, and means for uptaking the plate precursor within the cylinder.
They have also advantages in that, once the plate precursor in the roll form is stored within the cylinder, a printing plate can be automatically exchanged at a certain frequency.
These are printing presses having a plate cylinder as disclosed in, for example, U.S. Pat. No. 5,657,692. That is, as is shown in the schematic view of a plate cylinder in FIG. 1, the plate cylinder has, within the cylinder 1, a supply spool 3 with a plate precursor 2 wound therearound and an uptake spool 4 (both supply spool 3 and uptake spool 4 having their core). The plate cylinder has a construction in which the plate precursor is stored in the roll form on supply spool 3 within the cylinder, unrolled, withdrawn through an axial opening 1a, brought on the outer surface of the cylinder to wrap the cylinder, reintroduced through axial opening la into the cylinder, and received by uptake spool 4 within the cylinder.
Fixation of a plate precursor on the plate cylinder can be carried out, for example, by locking either one of the supply spool or the uptake spool not to rotate, applying a rotational torque in the rotational direction to the other spool to give a certain tension to the plate precursor, and then locking it.
Further, as in a printing press disclosed in Japanese Patent O.P.I. Publication Nos. 11-28802, which has a plate cylinder composed of two cylinders, one being an outer hollow cylinder having orifices and the other an inner cylinder, fixation of a plate precursor on the plate cylinder can be carried out by mounting the plate precursor on the outer, hollow cylinder, and then sucking air beneath the outer cylinder through the orifices.
However, commercially available waterless plate precursors used in the DI printing press require plate cleaning after laser irradiation for forming an image. This plate cleaning process results in an increase of preparation time for printing and a resultant cost increase.
In contrast, when a printing plate precursor capable of being developed on press (so-called an on-press type printing plate precursor) is used in the DI printing press employing a dampening water, printing can start without plate cleaning, which results in printing cost reduction due to shortening of the preparation time for printing.
The on-press type printing plate precursor comprises a layer which contains a water soluble material or a water swellable material and is capable of being removed on a plate cylinder of a printing press. This layer is dissolved in or swelled by, a dampening water from a dampening water supply device of a printing press to reduce its strength, and is removable.
This layer, when a plate precursor is mounted on a plate cylinder of a printing press, is continuous, and present at a plate fixing section, for example, at a plate gripping section of a printing press. Therefore, a printing plate prepared from the plate precursor has the problem that a dampening water penetrates to the plate gripping section during printing, dissolves or swells the layer at that section, reducing strength of the layer, which results in deterioration of plate fixing stability or plate gripping stability.
Further, a construction storing a plate precursor in the roll form within a plate cylinder of a printing press also has the problem that a dampening water penetrates to the surface of the plate precursor on the storing side, resulting in deterioration of performance of the plate precursor.
An object of the invention is to provide a printing method employing an on-press type printing plate precursor and improving a plate fixing stability and a registering accuracy, and to provide a printing method employing an on-press type printing plate precursor in the roll form stored within a plate cylinder of a printing press and minimizing deterioration of printing performance thereof. Another object of the invention is to provide a printing press capable of realizing the printing method described above.